Method for producing composite plated product

ABSTRACT

There is provided a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate by using a composite plating solution wherein carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added to a silver plating solution, the method being capable of preventing the wear resistance of the composite plated product from being deteriorated even if the current density in a plating process is increased. The molar ratio of silver to free cyanogen in the composite plating solution is adjusted so as not to be less than 0.7, preferably so as to be in the range of from 0.7 to 1.3. The silver matrix orientation adjusting agent contains selenium ions, and is preferably potassium selenocyanate. The concentration of the silver matrix orientation adjusting agent in the composite plating solution is adjusted so as to be in the range of from 5 mg/l to 20 mg/l.

TECHNICAL FIELD

The present invention generally relates to a method for producing a composite plated product. More specifically, the invention relates to a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate and which is used as a material of contact and terminal parts such as switches and connectors.

BACKGROUND ART

Conventionally, as materials of contact and terminal parts such as switches and connectors, there are used silver-plated products wherein a conductive material such as copper or a copper alloy is plated with silver in order to prevent oxidation of the conductive material due to heat in sliding processes.

However, there is a problem in that silver coatings are easily stripped by sliding since they are soft and easily wear and since they generally have a high coefficient of friction. In order to solve this problem, there is proposed a method for improving the wear resistance of a conductive material by electroplating the conductive material with a composite material wherein graphite particles are dispersed in a silver matrix (see, e.g., Japanese Patent Laid-Open No. 9-7445). There is also proposed a method for producing a silver coating, which contains graphite particles, by means of a plating bath to which a wetting agent suitable for the dispersion of graphite particles is added (see, e.g., Japanese Patent Unexamined Publication No. 5-505853 (National Publication of Translated Version of PCT/DE91/00241)). Moreover, there is proposed a method for coating carbon particles with a metal oxide or the like by the sol-gel method to enhance the dispersibility of the carbon particles in a composite plating bath of silver and the carbon particles to increase the quantity of carbon particles in a composite coating (see, e.g., Japanese Patent Laid-Open No. 3-253598).

However, composite plated products produced by the above-described conventional methods have a relatively high coefficient of friction and a relatively low wear resistance, so that there is a problem in that the composite plated products can not be used as the materials of long-life contacts and terminals. Therefore, it is desired to provide a composite plated product which has a larger content of carbon, a larger quantity of carbon particles on the surface thereof, and a better wear resistance than those of the composite plated products produced by the conventional methods.

For that reason, the inventors has proposed a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate, the composite plated product having a large content of carbon and a large quantity of carbon particles on the surface thereof and having a low coefficient of friction and an excellent wear resistance, by electroplating a substrate in a silver plating solution to which carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added (see Japanese Patent Application No. 2005-195678).

However, there is a problem in that the wear resistance of the composite plated product is deteriorated if the current density in the plating process is increased in order to improve the productivity of the composite plated product in the method proposed in Japanese Patent Application No. 2005-195678.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate by using a composite plating solution wherein carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added to a silver plating solution, said method being capable of preventing the wear resistance of the composite plated product from being deteriorated even if the current density in a plating process is increased.

In order to accomplish the aforementioned object, the inventors have diligently studied and found that it is possible to prevent the wear resistance of a composite plated product from being deteriorated even if the current density in a plating process is increased, if the molar ratio of silver to free cyanogen in a composite plating solution is adjusted in a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate by using a composite plating solution wherein carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added to a silver plating solution. Thus, the inventors have made the present invention.

A method for producing a composite plated product according to the present invention, comprises the steps of: preparing carbon particles and a silver matrix orientation adjusting agent which is an agent for adjusting the orientation of a silver matrix; treating the carbon particles by an oxidation treatment; adding the treated carbon particles and the silver matrix orientation adjusting agent to a silver plating solution to form a composite plating solution which contains the treated carbon particles and the silver matrix orientation adjusting agent; and electroplating a substrate in the composite plating solution to form a coating of a composite material, which contains the treated carbon particles in a silver layer, on the substrate, wherein the molar ratio of silver to free cyanogen in the composite plating solution is adjusted so as not to be less than 0.7, preferably so as to be in the range of from 0.7 to 1.3. In this method for producing a composite plated product, the silver matrix orientation adjusting agent preferably contains selenium ions, and is more preferably potassium selenocyanate. In addition, the concentration of the silver matrix orientation adjusting agent in the composite plating solution is preferably adjusted so as to be in the range of from 5 mg/1 to 20 mg/l. Moreover, the coating is preferably formed by electroplating the substrate at a current density of 1 to 3 A/dm².

A composite plating solution according to the present invention comprises: a silver plating solution for plating a substrate with silver; carbon particles treated by an oxidation treatment to be added to the silver plating solution; and a silver matrix orientation adjusting agent added to the silver plating solution, wherein the molar ratio of silver to free cyanogen in the composite plating solution is not less than 0.7.

According to the present invention, it is possible to prevent the wear resistance of a composite plated product from being deteriorated even if the current density in a plating process is increased, in a method for producing a composite plated product wherein a coating of a composite material containing carbon particles in a silver layer is formed on a substrate by using a composite plating solution wherein carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added to a silver plating solution. Therefore, it is possible to improve the productivity of the composite plated product. In addition, the composite plated product can be used as a material capable of sufficiently increasing the life of terminals such as switches and connectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for explaining an electric contact using a composite plated product according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In a preferred embodiment of a method for producing a composite plated product according to the present invention, the molar ratio of silver to free cyanogen (the molar ratio of silver/free cyanogen) in a composite plating solution, wherein carbon particles treated by an oxidation treatment and a silver matrix orientation adjusting agent are added to a silver plating solution, is adjusted to be 0.7 or more, preferably in the range of from 0.7 to 1.3, and the amount of the silver matrix orientation adjusting agent in the composite plating solution is preferably adjusted to be in the range of from 5 mg/l to 20 mg/l. This composite plating solution is used for electroplating a substrate, so that a coating of a composite material containing carbon particles in a silver layer is formed on the substrate.

In the preferred embodiment of a method for producing a composite plated product according to the present invention, lipophilic organic substances absorbed onto the surface of carbon particles are removed by the oxidation treatment before the carbon particles are added to a silver plating solution. Such lipophilic organic substances include aliphatic hydrocarbons, such as alkanes and alkenes, and aromatic hydrocarbons, such as alkylbenzene.

As the oxidation treatment for carbon particles, a wet oxidation treatment, or a dry oxidation treatment using oxygen gas or the like may be used. In view of mass production, a wet oxidation treatment is preferably used. If a wet oxidation treatment is used, it is possible to uniformly treat carbon particles having a large surface area.

As the wet oxidation treatment, there may be used a method for suspending carbon particles in an aqueous solution containing a conductive salt to put therein platinum electrodes or the like as a cathode and anode to carry out electrolysis, or a method for suspending carbon particles in water to add an optimum quantity of oxidizing agent thereto. In view of productivity, the latter is preferably used, and the quantity of carbon particles added to water is preferably in the range of from 1% to 20% by weight. The oxidizing agent may be nitric acid, hydrogen peroxide, potassium permanganate, potassium persulfate, sodium perchlorate or the like. It is considered that the lipophilic organic substances adhering to carbon particles are oxidized by the added oxidizing agent so as to be soluble in water to be suitably removed from the surface of the carbon particles. If the carbon particles treated by the wet oxidation treatment are filtered and washed, it is possible to further enhance the function of removing the lipophilic organic substances from the surface of the carbon particles.

The lipophilic organic substances, such as aliphatic and aromatic hydrocarbons, can be thus removed from the surface of the carbon particles by the above-described oxidation treatment. According to analysis based on gases heated at 300° C., gases generated by heating carbon particles to 300° C. after the oxidation treatment hardly contain lipophilic aliphatic hydrocarbons such as alkanes and alkenes, and lipophilic aromatic hydrocarbons such as alkylbenzenes. Even if the carbon particles after the oxidation treatment slightly contain aliphatic and aromatic hydrocarbons, the carbon particles can be dispersed in a silver plating solution. However, the carbon particles do not preferably contain hydrocarbons having a molecular weight of 160 or more, and the intensity (the intensity in purge and gas chromatography and mass spectroscopy) of gases generated at 300° C. from hydrocarbons having a molecular weight of less than 160 in the carbon particles is preferably 5,000,000 or less. It is considered that, if the carbon particles contain hydrocarbons having a large molecular weight, the surface of each of the carbon particles is coated with strong lipophilic hydrocarbons, and the carbon particles are coagulated in the silver plating solution which is an aqueous solution, so that the carbon particles do not form a coating of a composite material.

When carbon particles, from which aliphatic and aromatic hydrocarbons are removed by the above-described oxidation treatment, are suspended in the silver plating solution to carry out electroplating, a cyanide containing silver plating solution is preferably used as the silver plating solution. In the conventional methods, it is required to add a surface active agent to a silver plating solution if it is a cyanide containing silver plating solution. However, in the preferred embodiment of a method for producing a composite plated product according to the present invention, it is not required to add any surface active agents to the silver plating solution, since it is possible to obtain a composite plating solution wherein carbon particles are uniformly dispersed in the silver plating solution even if no surface active agent is added thereto. Furthermore, the concentration of carbon particles in the composite plating solution is preferably in the range of from 40 g/l to 200 g/l. If it is less than 40 g/l, the content of carbon particles in the composite coating is considerably decreased, and if it exceeds 200 g/l, the viscosity of the composite plating solution is increased, so that it is difficult to agitate the composite plating solution.

If a cyanide containing silver plating solution is used, it is possible to obtain a composite coating which has a large content of carbon and a large quantity of carbon particles on the surface thereof. It is considered that the reason why the content of carbon in the coating is increased is that carbon particles are easily incorporated into a silver matrix since the silver plating solution does not contain any surface active agents to prevent the surface active agents from being absorbed onto the growth surface of a silver plating crystal when the crystal grows. It is also considered that the reason why the quantity of carbon particles on the surface of the coating is increased is that it is difficult for the carbon particles to be removed from the surface of the coating (similar to the cleaning function of detergent) during washing after plating, since the silver plating solution does not contain any surface active agents.

If carbon particles treated by the oxidation treatment are thus added to a silver plating solution, it is possible to sufficiently disperse the carbon particles in the silver plating solution without using any additives such as dispersing agents and without coating the surface of the carbon particles. In addition, if such a silver plating solution is used for carrying out electroplating, it is possible to produce a composite plated product wherein a coating of a composite material containing the carbon particles in a silver layer is formed on a substrate, the composite plated product having a large content of carbon and a large quantity of carbon particles on the surface thereof and having an excellent wear resistance.

In the preferred embodiment of a method for producing a composite plated product according to the present invention, the cyanide containing silver plating solution preferably contains potassium silver cyanide (K[Ag(CN)₂]) and potassium cyanide (KCN). The concentration (X) of potassium silver cyanide in the cyanide containing silver plating solution is preferably in the range of from about 250 g/l to about 300 g/l, and the concentration (Y) of potassium cyanide in the cyanide containing silver plating solution is in the range of from about 80 g/l to about 120 g/l. The molecular weight of potassium silver cyanide is 199, and the molecular weight of potassium cyanide is 65.1. Therefore, the molar ratio (Z) of silver to free cyanogen (the molar ratio of silver/free cyanogen) is preferably in the range of from 0.7 to 1.3 ad derived from the expression z=(X/199)/(Y/65.1) If this ratio is less than 0.7, the orientation plane of the silver matrix is (111) plane to deteriorate the wear resistance of the composite plated product when the current density in the plating process is increased. On the other hand, if the molar ratio exceeds 1.3, it is difficult to dissolve potassium silver cyanide serving as the source of silver.

In the preferred embodiment of a method for producing a composite plated product according to the present invention, there is used a composite plating solution wherein a silver matrix orientation adjusting agent for adjusting the orientation of a silver matrix is added to a silver plating solution in addition to the carbon particles treated by the oxidation treatment. The silver matrix orientation adjusting agent preferably contains selenium (Se) ions, and is more preferably potassium selenocyanate (KSeCN). The concentration of the silver matrix orientation adjusting agent in the composite plating solution is preferably in the range of from 5 mg/l to 20 mg/l. If such a silver matrix orientation adjusting agent is added to the silver plating solution, the orientation of the silver matrix is considerably changed in accordance with the concentration of selenium ions. That is, the orientation plane of the silver matrix is (111) plane in conventional composite plated products coated with a composite material of silver and graphite particles. However, if the silver matrix orientation adjusting agent is added to the silver plating solution, the orientation plane of the silver matrix is changed to be (220) plane. It is considered that the coating is formed of fine crystal grains, so that the characteristics of the coating are greatly changed by the direction of growth of crystal grains. It is also considered that, if the crystal orientation of carbon particles in the composite material and the orientation of crystal grains in the silver matrix are optimum, the silver matrix is easily deformed by friction and sliding, and the coefficient of friction is greatly decreased in cooperation with the lubricity of carbon particles, so that the wear resistance of the composite plated product is improved.

It is considered that the composite coating of silver and carbon particles, wherein the orientation plane of a silver matrix is (220) plane, is formed by adding selenium ions to the composite plating solution containing carbon particles dispersed therein without adding any surface active agents. That is, in conventional composite coatings which contain graphite particles in the silver layer, a surface active agent is added to a silver plating solution in order to sufficiently disperse carbon particles therein. However, it is considered that the surface active agent is also absorbed onto the composite coating to have an influence on the direction of growth of the silver matrix, so that it is difficult to obtain a composite coating wherein the orientation plane of a silver matrix is (220) plane.

By thus forming a composite coating wherein the orientation plane of the silver matrix is (220) plane, the composite coating can have a lower coefficient of friction. That is, if a silver plating solution containing a surface active agent is used as conventional methods, it is not possible to obtain a composite coating wherein the orientation plane of a silver matrix is (220) plane. Therefore, the coefficient of friction of any one of the composite coating products produced by conventional methods is higher than that of a composite coating product produced by the preferred embodiment of a method for producing a composite plated product according to the present invention, and the wear resistance thereof is lower than that of a composite coating product produced by the preferred embodiment of a method for producing a composite plated product according to the present invention.

By the above-described preferred embodiment of a method for producing a composite plated product according the present invention, it is possible to produce a composite plated product wherein a coating of a composite material containing 1.7 to 2.5% by weight of carbon particles in a silver layer is formed on a substrate, the quantity of the carbon particles on the surface thereof (the rate of carbon particles coating the substrate) being 25% by area or more, and the orientation plane of a silver matrix being (220) plane. Furthermore, the wear resistance of the composite plated product is improved as the content of carbon in the composite coating is increased. In a composite plated product produced by the above-described preferred embodiment of a method for producing a composite plated product according to the present invention, the content of carbon in the coating can be 1.7 to 2.5% by weight, and the quantity of carbon particles on the surface of the coating can be 25% by area or more, although the quantity of carbon particles on the surface of the coating is about 5% by area in conventional composite plated products of silver and graphite. Therefore, it is possible to obtain a composite plated product having an excellent wear resistance. In addition, since the orientation plane of the silver matrix is (220) plane, it is possible to obtain a composite plated product having a coefficient of friction, which is greatly decreased in cooperation with the lubricity of carbon particles, and having an excellent wear resistance.

The thickness of the composite plated product is preferably in the range of from 2 μm to 10 μm. If the thickness of the composite plated product is less than 2 μm, the wear resistance thereof is insufficient, and if it exceeds 10 μm, the production efficiency thereof is bad.

In an electric contact comprising a stationary contact 10 and a movable contact 12 which is slidable on the stationary contact 10 in directions shown by arrow A in FIG. 1, if at least one of the stationary contact 10 and the movable contact 12 is formed of a composite plated product according to the present invention, the electric contact can have an excellent wear resistance. In this case, only a part of one of the stationary contact 10 and the movable contact 12 contacting the other contact may be formed of a composite plate product according to the present invention.

Examples of a method for producing a composite plated product according to the present invention will be described below in detail.

Examples 1 and 2

First, 6% by weight of scale-shaped graphite particles (Carbon SN-5 produced by SEC Corporation) having a mean particle diameter of 5 μm were prepared as carbon particles to be added to 3 liters of pure water. The mixed solution thus obtained was heated to 50° C. while being stirred. Then, 1.2 liters of a solution containing 0.1 mol/l of potassium persulfate was prepared as an oxidizing agent to be gradually dropped to the mixed solution, and then, stirred for two hours to carry out an oxidation treatment. Thereafter, filtration was carried out by means of a filter paper, and washing was carried out.

With respect to carbon particles before and after the oxidation treatment, gases generated at 300° C. were analyzed by means of a purge and gas chromatography and mass spectrometer (Japan Analysis Industry JHS-100) (GCMAS QP-5050A produced by Shimadzu Corp.). As a result, it was found that lipophilic aliphatic hydrocarbons, such as nonane, decane and 3-methyl-2-hepten, and lipophilic aromatic hydrocarbons, such as xylene, were removed from the carbon particles by the above-described oxidation treatment.

Then, 80 g/l of carbon particles treated by the above-described oxidation treatment were added to a cyanide containing silver plating solution comprising 280 g/l of potassium silver cyanide and 90 g/l of potassium cyanide, the molar ratio of silver/free cyanogen in the cyanide containing silver plating solution being 1.01. After the carbon particles were thus dispersed and suspended therein, 12 mg/l of potassium selenocyanate serving as a silver matrix orientation adjusting agent was added thereto to prepare a composite plating solution of silver and carbon particles. This composite plating solution was used for electroplating a copper plate serving as a raw material having a thickness of 0.3 mm at a temperature of 25° C. and at a current density of 1 A/dm² (Example 1) and 3 A/dm² (Example 2), respectively, to produce a composite plated product wherein a composite coating of silver and carbon particles having a thickness of 5 μm was formed on the copper plate. Furthermore, in order to improve the adhesion of the coating, silver strike plating was carried out as underlayer plating at a temperature of 25° C. and at a current density of 3 A/dm² in a silver strike plating bath containing 3 g/l of potassium silver cyanide and 100 g/l of potassium cyanide.

Samples were cut out of the composite plated product (containing the raw material) to be prepared for analyses of Ag and C, respectively. The content by weight (X wt %) of Ag in the sample was obtained by the plasma spectroscopic analysis by means of an ICP device (IRIS/AR produced by Jarrell Ash Corporation), and the content by weight (Y wt %) of C in the sample was obtained by the infrared analysis by means of a carbon/sulfur microanalyzer (EMIA-U510 produced by HORIBA, Ltd.). Then, the content by weight of C in the coating was calculated as Y/(X+Y). As a result, the content by weight of C in the coating was 2.1% and 2.5% by weight in Examples 1 and 2, respectively.

The surface of a test piece cut out of each of the composite plated products was observed, and the quantity (% by area) of carbon particles on the surface of the coating of the test piece was calculated as follows. First, an image of the surface of the test piece was taken as a super depth image at an objective lens power of 100 by means of a super depth shape microscope (VK-8500 produced by KEYENCE CORPORATION). Then, an image analyzing application (SCION IMAGE produced by SCION CORPORATION) was used on a personal computer for incorporating the image as a monochrome to indicate the contrast of the image as binary digits, so that the portions of silver were separated from the portions of carbon particles. Then, the quantity of carbon particles on the surface of the coating was calculated as a ratio Y/X of the number (Y) of pixels of the portions of carbon particles to the number (X) of pixels of the whole image. As a result, the quantity of carbon particles on the surface of the coating was 32% to 34% by area in Examples 1 and 2, respectively.

Then, the orientation of the silver matrix of a test piece cut out of each of the composite plated products was evaluated. In the evaluation of the orientation of the silver matrix, an X-ray diffractometer (XRD) (RAF-rB produced by RIGAKU Corporation) was used for measuring X-ray diffraction peaks, and the plane orientation of the strongest peak of the silver matrix was evaluated as the orientation of crystal of the coating. Furthermore, Cu—Kα was used as a vessel for measuring the X-ray diffraction peaks at 50 kV and 100 mA. In addition, a scintillation counter, a wide angle goniometer, and a curved crystal monochromator were used. The scanning range 2θ/θ was in the range of from 10° to 90°, and the step width was 0.05°. The scanning mode was FT, and the sampling time was 1.00 second. As a result, the orientation plane of the silver matrix was (220) plane in Examples 1 and 2.

One of two test pieces cut out of each of the composite plated products thus obtained was intended (R=3 mm) to be used as an indenter, and the other test piece was used as an evaluating sample, so that the wear resistance of each of the composite plated products was evaluated by confirming the wearing state of each of the composite plated products by continuing the reciprocating sliding movement (sliding distance: 10 mm, sliding speed: 2.5 Hz) of the indenter while pushing the indenter against the evaluating sample at a constant load (0.5 N) until the raw material was exposed. As a result, in Examples 1 and 2, the raw material was not exposed after the reciprocating sliding movement was repeated 500,000 times or more.

Examples 3 and 4

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 16 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Examples 3 and 4, the content of carbon particles was 1.6% and 2.4% by weight, respectively, and the quantity of carbon particles on the surface was 33% and 35% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane. Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times.

Examples 5 and 6

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that there was used a cyanide containing silver plating solution comprising 240 g/l of potassium silver cyanide and 90 g/l of potassium cyanide, the molar ratio of silver/free cyanogen in the cyanide containing silver plating solution being 0.87, and that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 8 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Examples 5 and 6, the content of carbon particles was 2.0% and 1.8% by weight, respectively, and the quantity of carbon particles on the surface was 32% and 31% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane. Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times.

Examples 7 and 8

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that there was used a cyanide containing silver plating solution comprising 240 g/l of potassium silver cyanide and 90 g/l of potassium cyanide, the molar ratio of silver/free cyanogen in the cyanide containing silver plating solution being 0.87. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Examples 7 and 8, the content of carbon particles was 1.9% and 2.3% by weight, respectively, and the quantity of carbon particles on the surface was 31% and 33% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane. Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times.

Comparative Examples 1 and 2

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that there was used a cyanide containing silver plating solution comprising 100 g/l of potassium silver cyanide and 120 g/l of potassium cyanide, the molar ratio of silver/free cyanogen in the cyanide containing silver plating solution being 0.27, and that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 4 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Comparative Examples 1 and 2, the content of carbon particles was 2.2% and 1.7% by weight, respectively, and the quantity of carbon particles on the surface was 34% and 22% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane in Comparative Example 1 wherein electroplating was carried out at a current density of 1 A/dm², whereas the orientation plane of the silver matrix was (111) plane in Comparative Example 2 wherein electroplating was carried out at a current density of 3 A/dm². Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times in Comparative Example 1 wherein electroplating was carried out at a current density of 1 A/dm², whereas the substrate was exposed after the reciprocating sliding movement was repeated about 480,000 times in Comparative Example 2 wherein electroplating was carried out at a current density of 3 A/dm².

Comparative Examples 3 and 4

Composite plated products were produced by the same method as that in Comparative Examples 1 and 2, respectively, except that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 8 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Comparative Examples 3 and 4, the content of carbon particles was 2.0% and 1.5% by weight, respectively, and the quantity of carbon particles on the surface was 27% and 21% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane in Comparative Example 3 wherein electroplating was carried out at a current density of 1 A/dm², whereas the orientation plane of the silver matrix was (200) plane in Comparative Example 4 wherein electroplating was carried out at a current density of 3 A/dm². Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times in Comparative Example 3 wherein electroplating was carried out at a current density of 1 A/dm², whereas the substrate was exposed after the reciprocating sliding movement was repeated about 420,000 times in Comparative Example 4 wherein electroplating was carried out at a current density of 3 A/dm².

Comparative Examples 5 and 6

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that there was used a cyanide containing silver plating solution comprising 185 g/l of potassium silver cyanide and 90 g/l of potassium cyanide, the molar ratio of silver/free cyanogen in the cyanide containing silver plating solution being 0.67, and that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 4 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Comparative Examples 5 and 6, the content of carbon particles was 1.8% and 1.7% by weight, respectively, and the quantity of carbon particles on the surface was 33% and 28% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane in Comparative Example 5 wherein electroplating was carried out at a current density of 1 A/dm², whereas the orientation plane of the silver matrix was (200) plane in Comparative Example 6 wherein electroplating was carried out at a current density of 3 A/dm². Moreover, the substrate was exposed after the reciprocating sliding movement was repeated about 480,000 times in Comparative Example 5 wherein electroplating was carried out at a current density of 1 A/dm², and the substrate was exposed after the reciprocating sliding movement was repeated about 310,000 times in Comparative Example 6 wherein electroplating was carried out at a current density of 3 A/dm².

Comparative Examples 7 and 8

Composite plated products were produced by the same method as that in Comparative Examples 5 and 6, respectively, except that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 12 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Comparative Examples 7 and 8, the content of carbon particles was 1.8% and 1.6% by weight, respectively, and the quantity of carbon particles on the surface was 31% and 21% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane in Comparative Example 7 wherein electroplating was carried out at a current density of 1 A/dm², whereas the orientation plane of the silver matrix was (111) plane in Comparative Example 8 wherein electroplating was carried out at a current density of 3 A/dm². Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times in Comparative Example 7 wherein electroplating was carried out at a current density of 1 A/dm², whereas the substrate was exposed after the reciprocating sliding movement was repeated about 370,000 times in Comparative Example 8 wherein electroplating was carried out at a current density of 3 A/dm².

Comparative Examples 9 and 10

Composite plated products were produced by the same method as that in Examples 1 and 2, respectively, except that the amount of potassium selenocyanate added as a silver matrix orientation adjusting agent was 4 mg/l. With respect to the composite plated products thus obtained, the content of carbon particles in the coating, and the quantity (% by area) of carbon particles on the surface of the coating were calculated by the same methods as those in Examples 1 and 2, and the orientation of the silver matrix and the wear resistance thereof were evaluated by the same methods as those in Examples 1 and 2. As a result, in Comparative Examples 9 and 10, the content of carbon particles was 1.9% and 1.7% by weight, respectively, and the quantity of carbon particles on the surface was 31% and 27% by area, respectively. In addition, the orientation plane of the silver matrix was (220) plane in Comparative Example 9 wherein electroplating was carried out at a current density of 1 A/dm², whereas the orientation plane of the silver matrix was (111) plane in Comparative Example 10 wherein electroplating was carried out at a current density of 3 A/dm². Moreover, the substrate was not exposed after the reciprocating sliding movement was repeated over 500,000 times in Comparative Example 9 wherein electroplating was carried out at a current density of 1 A/dm², whereas the substrate was exposed after the reciprocating sliding movement was repeated about 370,000 times in Comparative Example 10 wherein electroplating was carried out at a current density of 3 A/dm².

The results in Examples 1 through 8 and Comparative Examples 1 through 10 are shown in Tables 1 and 2.

TABLE 1 Current [Ag(CN)₂] KCN KSeCN Density (g/L) g/L) Ag/CN (mg/L) (A/dm²) Ex. 1 280 90 1.01 12 1 Ex. 2 280 90 1.01 12 3 Ex. 3 280 90 1.01 16 1 Ex. 4 280 90 1.01 16 3 Ex. 5 240 90 0.87 8 1 Ex. 6 240 90 0.87 8 3 Ex. 7 240 90 0.87 12 1 Ex. 8 240 90 0.87 12 3 comp. 1 100 120 0.27 4 1 comp. 2 100 120 0.27 4 3 comp. 3 100 120 0.27 8 1 comp. 4 100 120 0.27 8 3 comp. 5 185 90 0.67 4 1 comp. 6 185 90 0.67 4 3 comp. 7 185 90 0.67 12 1 comp. 8 185 90 0.67 12 3 comp. 9 280 90 1.01 4 1 comp. 10 280 90 1.01 4 3

TABLE 2 Quantity Content of Carbon of C Particles Crystal (% by on Surface Orien- Wear Weight) (% by area) tation Resistance Ex. 1 2.1 32 220 over 500,000 Ex. 2 2.5 34 220 over 500,000 Ex. 3 1.6 33 220 over 500,000 Ex. 4 2.4 35 220 over 500,000 Ex. 5 2.0 32 220 over 500,000 Ex. 6 1.8 31 220 over 500,000 Ex. 7 1.9 31 220 over 500,000 Ex. 8 2.3 33 220 over 500,000 comp. 1 2.2 34 220 over 500,000 comp. 2 1.7 22 111 about 480,000 comp. 3 2.0 27 220 over 500,000 comp. 4 1.5 21 200 about 420,000 comp. 5 1.8 33 220 about 480,000 comp. 6 1.7 28 200 about 310,000 comp. 7 1.8 31 220 over 500,000 comp. 8 1.6 21 111 about 370,000 comp. 9 1.9 31 220 over 500,000 comp. 10 1.7 27 111 about 370,000 

1. A method for producing a composite plated product, the method comprising the steps of: preparing carbon particles and a silver matrix orientation adjusting agent which is an agent for adjusting the orientation of a silver matrix; treating said carbon particles by an oxidation treatment; adding the treated carbon particles and said silver matrix orientation adjusting agent to a silver plating solution to form a composite plating solution which contains the treated carbon particles and the silver matrix orientation adjusting agent; and electroplating a substrate in said composite plating solution to form a coating of a composite material, which contains the treated carbon particles in a silver layer, on the substrate, wherein the molar ratio of silver to free cyanogen in said composite plating solution is adjusted so as not to be less than 0.7.
 2. A method for producing a composite plated product as set forth in claim 1, wherein said molar ratio of silver to free cyanogen in said composite plating solution is adjusted so as to be in the range of from 0.7 to 1.3.
 3. A method for producing a composite plated product as set forth in claim 1, wherein said silver matrix orientation adjusting agent contains selenium ions.
 4. A method for producing a composite plated product as set forth in claim 1, wherein said silver matrix orientation adjusting agent is potassium selenocyanate.
 5. A method for producing a composite plated product as set forth in claim 3, wherein the concentration of said silver matrix orientation adjusting agent in said composite plating solution is adjusted so as to be in the range of from 5 mg/l to 20 mg/l.
 6. A method for producing a composite plated product as set forth in claim 1, wherein said coating is formed by electroplating the substrate at a current density of 1 to 3 A/dm².
 7. A composite plating solution comprising: a silver plating solution for plating a substrate with silver; carbon particles treated by an oxidation treatment to be added to the silver plating solution; and a silver matrix orientation adjusting agent added to the silver plating solution, wherein the molar ratio of silver to free cyanogen in the composite plating solution is not less than 0.7. 